Producing and concentrating diolefins



Sephli', 946. F. E. FREY ET AL PRODUCING AND CONCENTRATING DIOLEFINS Original Filed April 1, 194

wwzmzkdm d UZEbm twOazOuwo zockzwuomoiwo INVENTOR FREDERICK E.FREY

BY ROBERT D smw r W AT ORN Y Patented Sept. 17, 1946 UNITED STATES PATENT OFFICE PRODUCING AND CONCENTRATING DIOLEFIN S Frederick E. Frey, Bartlesville, kla., and Robert D. Snow, Edgewood,

Md., assignors to Phillips Petroleum Company, a corporation of Delaware 16 Claims. 1 t

This invention relates to processes for obtaining conjugated diolefins in a concentrated form from hydrocarbon mixtures. It relates further to the concentration of low boiling diolefins, more particularly cyclopentadiene, butadiene, and its lower boiling homologues, from mixtures containing other hydrocarbons of closely adjacent boiling points. production of a mixture of substantially normal C4 hydrocarbons by the dehydrogenation of normal butane and/or normal butenes and the separation of a butadiene concentrate therefrom.

Diolefins are produced in a number of ways which include cracking of heavier oils, pyrolysis of gaseous hydrocarbons other than methane, the copolymerization of acetylene and ethylene to form bu'tadiene, catalytic and thermal conversion of alcohols, both of the same number of carbon atoms per molecule as the desired 'diolefin and of a fewer number of carbon atoms per molecule, and other more or less involved chemical processes, as well as the dehydrogenation of the corresponding olefins which in turn may have been produced by the dehydrogenation of the corresponding paraffins. Although this latter procedure is one of the more direct ways of producing diolefins it has not yet found very extensive commercial application, and one of the obstacles in its commercial development has been the dimculty of effecting separation of olefins and diolefins from each other and from mixtures containing the corresponding paraifins.

Various processes have been proposed for the separation of conjugated diolefins by means of their reactions with sulfur dioxide. Anilin Und Soda-Fabrik, German Pat. 236,386 (1911) disclosed the fact that conjugated diolefins react with gaseous sulfur dioxide or aqueous sulfurous acid at ordinary temperature to give mainly an They stated that when the amount of S02 present was small or the reaction time short, the product was partly soluble in water, and the soluble part crystallized in needle crystals which decomposed easily on heating to regenerate the di-.

olefin and S02. They suggested this reaction as a means of separating diolefins.

Matthews and Strange, U. S. 1,196,259 (1916) disclosed a'process for the purification of diolefins by reaction with sulfur dioxide in the presence of halogen-containing compounds which they claimed served to promote the formation of the crystalline material. The only temperature cited was 42 C. They considered this soluble,

crystalline material, which decomposed at 120 C.,

to be a sulfoxide.

Staudinger, German 506,839 (1930), taught that the easily decomposed crystalline compound was a monomeric cyclic sulfone formed by 1-4 addition, and that the insoluble amorphous com- As one modification, it relates to the Badische'.

insoluble, amorphous compound.

(Cl. 260-r-329) pound was a polymeric sulfone. He disclosed a process for the preparation of the crystalline monomeric sulfone in which the reaction of the diolefin with S02 was carried out at room tem- 5 perature in the presence of anti-catalysts such as polyhydric phenols which inhibited the formation of the polysulfone.

Perkins (Canadian Patent 329,043 (1933) and U. S. 1,993,681 (1935)), disclosed a process for separating diolefins from hydrocarbon mixtures by heating the mixture with less than half its weight of sulfur dioxide for prolonged periods of time at about 100 C. The process described by Perkins may be continuous or stepwise with respect to the removal of the crystalline addition product and the return of the sulfur dioxide to the reactor, but is definitely a batch process with respect to the hydrocarbon mixture treated.

We have now found that conjugated diolefins by reacting with sulfur dioxide at 60-80" C., with or without materials such as isobutylene, and polyhydric phenols which inhibit the formation of the heteropolymeric sulfone addition product and with or Without catalysts which promote the formation of the monomeric sulfone, the said process being continuous with respect to the flow of hydrocarbon and continuous or stepwise with respect to the separation of the diolefin-SOz addition product.

An object of this invention is to concentrate conjugated diolefins, particularly butadiene, by separation from other hydrocarbons of similar boiling temperatures in a continuous manner.

Another object is to produce a butadiene concentrate from mixtures of hydrocarbons containing relatively low concentrations of butadiene such as are produced by cracking or dehydrogenation.

Another object is to furnish a method by which a conjugated diolefin product, previously concentrated by some other process, can be further freed of diluent parafiin and olefin hydrocarbons and other undesirable impurities.

Another object is to separate a mixture of paraffin, monoolefin and diolefin hydrocarbons into three fractions consisting of the respective classes of hydrocarbons, each in concentrated form.

Another object is to combine methods for separating butadiene, butenes and butane from hydrccarbo-n mixtures with two-stage catalytic dehydrogenation with cycling of the butane and butenes to the first and second stages, respective- 55 1y, of the dehydrogenation process in order to obtain high yields of butadiene from n-butane or a C4 fraction.

Another object is to increase the concentration of butenes in the charge stock going to the sec- 60 0nd stage of a two-stage dehydrogenation procmay be separated from mixtures containing them ess for producing butadiene from normal butane in order to improve the efficiency of th second stage.

Further objects will become evident to those skilled in the art as the description of the process proceeds.

It has been disclosed in U. S. Patent 2,186,524, of which we are coinventors, that sulfur dioxide form minimum-boiling azeotropic mixtures with each of the butanes and butenes. In the copending application of Frederick E. Frey, Serial No. 383,235, filed March 13, 1941, it has been disclosed that butadiene may be separated from accompanying C4 hydrocarbons by a limited azeotropic distillation in the presence of sulfur dioxide, with separation of a kettl product containing butadiene and Z-butenes, and substantially free of sulfur dioxide, the distillation being carried out so that there is a minimum of, or no, chemical reaction between sulfur dioxide and any unsaturated hydrocarbons present. We have now found that butadien may be separated from such a kettle product by a process involving reacting the butadiene with sulfur dioxide to form a monomeric sulfon'e, particularly when this is done under novel conditions elsewhere herein more fully discussed. We have further found that in our present process the initial distillation in the presence of sulfur dioxide may be advantageously carried out under conditions such that a substantial portion, if not all, of the diolefin material present, such as butadiene, is reacted with sulfur dioxide to form a monomeric sulfone.

We have found that temperatures of 60-80 C. are sufficiently high to effectively suppress the formation of undesirable heteropolymeric sulfones of either th monoolefins or diolefins normally present and yet also suiiiciently high to give a suitable reaction rate to the formation of the desirable monomeric sulfone. However, particularly when operating in the lower part of the temperature range, which is more favorable to the separation of paraffins by azeotropic distillation, we may use inhibitors of the branched chain olefin type such as isobutylene or unsym-methyl ethyl ethylene in amounts corresponding to 2 to per cent or more of the total hydrocarbons present, or very small proportions of typical antioxidant inhibitors of the type of polyhydric phenols, etc., well known to those skilled in the art to prevent polymeric sulfone formation, and we may use a catalyst to accelerate monomeric sulfone formation. However, in most cases it is unnecessary to use catalysts or inhibitors in the specified temperature range.

In its simplest form the present invention comprises continuous feeding of a liquid hydrocarbon mixture with one-half to three times its weight of liquid sulfur dioxide into a reaction chamber maintained at 60-80" 0., said reaction chamber being of such capacity as to allow time for completion of the reaction, and distilling the volatile matter from the stream emerging from the reactor at temperatures not exceeding 100 C. The sulfone addition product obtained as a residue may thereafter be decomposed by heating to 120-130 C. and S02 can then be extracted from the gaseous products by well known methods. This process is suitable for general application to the lower conjugated diolefins, espedrocarbon material which contains butadiene,

and which may be derived from any suitable source such as a fraction obtained from the gases resulting from the cracking of heavier oils or in the cracking of light gases to form normally gaseous olefins and/or low boiling diolefins, is charged through pipe i0 controlled by a valve ll to suitable fractionation equipment illustrated by fractionating column i2. In fractionating column I2 a distillation of the C4 hydrocarbons takes place in the presence of sulfur dioxide,

' which is added to the system through a pipe I3 cially butadiene, piperylene, isoprene, dimethyl- A and which may be introduced into a 1oWer-por-. tion of the fractionating column l2 through valve 7 I4 or which may be introduced entirely or in part at some suitable point above the point of introduction of C4 hydrocarbons through pipe [0 by being passed from pipe 3 through pipe I5 controlled by valve IS. The fractionating column l2 contains suitable packing or bubble plates, not shown, to aid in fractionation and is suitably heated at the bottom by heating means illustrated by heating coil l 1, and suitable and cooling reflux is obtained at the top by means such as is illustrated by the cooling coil 18. In one modification the fractionation is so conducted that substantially all of the unsaturated hydrocarbons are concentrated in the lower part, and only saturated hydrocarbons are removed in the overhead stream. Although the fractionating column can be operated over a fairly wide range of temperature, it has been found convenient to operate with a kettle temperature of about 80 C. and a head temperature of about 60 C. The amount of sulfur dioxide added to the fractionating column should be at least sufficient in quantity to form azeotropic mixtures with substantially all the parafiin hydrocarbons and to pass from fractionatingcolumn l2 with them as overhead low boiling fraction. As will be recognized by those skilled in the art the minimum sulfur dioxide requirement will vary with the composition of the hydrocarbon mixtur introduced to the fractionating column and with the conditions under which the column is operated. When treating a C4 hydrocarbon mixture, the amount of sulfur dioxide will generally be of the order of 2 to 3 mols of sulfur dioxide per mol of butane plus isobutane, more specifically about 2.5 mols. In many instances we prefer to hav a sufficient excess of sulfur dioxide over this amount to have an appreciable proportion thereof in the kettle product.

A low boiling fraction comprising sulfur di.

treatment in the system, and for this purpose it is passed from pipe 20 through pipe 22 controlled by valve 23 to separating unit 2 2. This separating unit 24 will comprise suitable equipment for recovering a normal butane stream, a

In many instances, however, it will sulfur dioxide stream, and for removing and discharging from the system other materials which may be present in the low-boiling material passing through pipe 2!} which are not desired in the system. Such separation equipment may consist of means for scrubbing the gases with water and recovery from the water of sulfur dioxide in a manner similar to that employed in the production of liquid sulfur dioxide; or it may comprise a refrigerating coil or vessel to cool the overhead mixture below a critical solution temperature together with a separator from which a light liquid layer may be removed to a fractionating column, and also from which a sulfur dioxide fraction may be recovered. The fractionating column can then be so operated that a substantially pure paraffin is removed as a kettle product and a parafiin-sulfur dioxide azeotrope is taken overhead and recycled to the aforesaid means for cooling and separation of liquid layers. In connection with such equipment the sulfur dioxide layer may if desired be passed to still another fractionating column, from which an azeotropic mixture is taken overhead and also recycled to the said cooling and separating means while sulfur dioxide is recovered in a fairly pure state as a kettle product.

A sulfur dioxide fraction may be removed from separating unit 24 through pipe 25 controlled by a valve 26. A portion of this material may be returned directly to the top part of fractionating column l2 as reflux by means not shown and/or to the fractionating column l2 through pipe !3. Undesired light gases may be removed from separating unit 24 and from the system through pipe 2i controlled by a valve 23.

The kettle product of fractionating column l2 will consist mainly of butenes, butadiene and/or a monomeric butadiene-sulfone, which latter may have been formed in the fractionating column, together with some excess sulfur dioxide. If the fractionating column 82 is so operated that substantial formation of this butadiene-sulfone takes place, it may be found desirable to have a small amount of an inhibitor present to prevent any substantial formation of heteropolymeric compounds of high molecular weight. When such inhibitors as isobutylene are not present in the material charged through pipe ll, or are-not present in sufficient quantities, such inhibiting material may be added to fractionating column l2 through pipe 30 controlled by a valve 3!; other inhibiting materials discussed herein may likewise be added in this manner as and when desired. The kettle product is removed from fractionating column i2 through pipe 32 controlled by valve and when little or no butadiene-sultone is contained therein, this material may be passed through valve 34 to a reaction chamber 35 wherein substantially all of the butadiene is converted to the monomeric sulfone. When sufficient sulfur dioxide is not present in this stream, additional quantities may be added from pipe 13 through pipe 4o controlled by a valve 41, which passes to pipe 32. When a butadiene-containing material is available which is not unduly diluted with but-ones or the like, this material may be added directly to reaction chamber 35 through pipe 42 controlled by a valve 13, the material being passed through pipes All and 32 to reaction chamber 35, and in some instances such a fraction may constitute the sole charge to the process. The amount of sulfur dioxide added to reaction chamber 35 should be molecularly equivalent to the unreacted butadiene present plus an excess 6 which may be per cent or more in excess of that quantity. The reaction chamber 35 is of suificient capacity to allow time for substantially complete reaction of butadiene with sulfur dioxide and is preferably maintained at a reaction temperature in the range of about 60 to 80 C. by a temperature controlling means not shown. The reaction chamber may be arranged so that the kettle product from the column enters at the bottom through pipe 32 as shown with the reaction mixture being Withdrawn from the top through pipe 4% controlled by a valve 41 and passed to a flash vaporizer 53. In some instances it may be found more desirable to have the charge material enter at the top and the reaction eiiiuent withdrawn entirely from the bottom in which case the material passing through pipe 32 is passed through pipe 44 controlled by a valve 45 leading to the top part of reaction chamber 35 and the reaction mixture will then be withdrawn from the bottom of the reaction chamber through pipe 5| controlled by valve 52 leading to pipe 46.

The operation of the fractionating column I2 is such as to permit concentration of butadiene and sulfur dioxide in the bottom portion and, as stated, a reaction between these materials to form a monomeric ulfone may be effected within this fractionating column. When this is done the separation of other materials from the butadiene is facilitated since the butadiene is being removed as such by chemical reaction, and the sulfone so produced can, therefore, be removed relatively free of unreacted butadiene which is maintained in the lower portion of the fractionating column and subsequently reacted. When such operating conditions are followed the material withdrawn through pipe 32 will contain very little unreacted butadiene and may be passed therefrom through pipe 3% controlled by a valve 3'! directly to flash vaporizer 58 for subsequent treatment, with elimination from the system of the reaction chamber 35.

The flash vaporizer so is preferably operated under a low absolute pressure and at a small elevated temperature which should be substantially below the decomposition temperature of the butadiene-sulfone which is in the neighborhood of about C. Unreacted material which will comprise primarily sulfur dioxide and butenes together with possible small amounts of butane are removed from flash vaporizer 55 through pipe 53 controlled by a valve 54 which leads to compressor 55. This compressor 55 serves to maintain a low absolute pressure within the flash vaporizer and to remove vapors and gases evolved therefrom as fast as they are released. These gases and vapors may be discharged from the system through pipe 5% controlled by a valve 5'! or may be passed entirely or in part through pipe 58 controlled by valve 59 to a separating unit 60. This separatin unit 60 will also comprise suitable equipment for effecting a separation of the materials charged thereto into any suitable or desirable fractions which will generally comprise at least a normal butene fraction and a sulfur dioxide fraction. together with. any heavy materials that may be present. Sulfur dioxide may be removed through a pipe 6| controlled by a valve '52, and undesired heavy materials may be removed through a pipe 63 controlled by a valve 64.

The butadienasulfone which will generally be present as a liquid under the preferred conditions discussed above is maintained at a somewhat elerange of about llil" to 130 0, preferably about 120 C., for a period of time sufilcient to efiect substantially complete decomposition, but for a time so limited that only a minimum of secondary reactions take place. The products of this decomposition are passed from heating coil l8 through a pipe "I2 controlled by a valve I3 to suitable separating means If: illustrated by the scrubber shown. Sulfur dioxide is separated from butadiene by suitable means as by Washing the gases with water introduced through pipe l6 controlled by valve '5? to a spray nozzle "it. A sulfur dioxide solution is removed from the lower part of the scrubber '55 through a pipe controlled by a valve 8i and butadiene in a relatively pure state is removed as a gas through a pipe 82 controlled by a Valve t3 and may be passed to suitable storage or further purification equipment as may be desired. Any undecomposed butadiene-sulfone present in th material passing through pipe l2 may be removed from the separating means i and reintroduced to pipe 659 by means not shown.

While this part of our invention may be operated as described for the purification of butadiene obtained from any suitable source, this separation treatment is advantageously combined with one or more dehydrogenation steps for the production of butadiene from normal butane and/ or from normal butenes and such a cooperative combination of process steps is to be considered a part of our invention. A normal butane fraction obtained from the material passing from the fractionating column I2 is removed from separating unit 24 through a pipe 913 controlled by a valve iii and passed to a dehydrogenation unit 82. This material may be joined by normal butane secured from any suitable source and introduced to the system through pipe 93 controlled by a valve 9%, and at times normal butane may be so introduced to our process as the sole charge. The eflluent of the dehydrogenation is passed through a pipe 95 controlled by a valve 96 to separating means 9? which may be of a simple type to separate C3 and lighter material from C4 hydrocarbons. Hydrogen and other material lighter than C"; hydrocarbons are removed from separator 81 through a pipe I to controlled by a valve til 5. C4 hydrocarbons are removed through pipe 582. If any material heavier than C4 hydrocarbons is present in the efiluent of the dehydrogenation, this may be removed through pipe m3 controlled by a valve m4, but in many instances such a removal of heavier material will not be necessary. When the dehydrogenation in unit 92 is such that substantial amounts of butadiene are present in the effluent, the C4 fraction may be passed through pip Hi2 and, valve I05 to pipe Ills and through valve It)? to pipe I9 and fractionating column I2 for treatment as has been discussed. When this modification is followed it may be desirable to operate fractionating column I2 so that a substantial portion of the butenes is contained in the material passing through pipe as and in the material passed through pipe 9E1. Such a single stage of dehydrogenation will be similar to that disclosed by Frederick E. Frey in his ccpending application Serial No. 354,890, filed August 30, 1940, or his hereinbefore mentioned application Serial No. 383,235, filed March 13, 1941. In many instances, however, it will be desirable to conduct the dehydrogenation unit 92 in a manner such as to produce optimum yields of butenes with little if any production of butadiene, with subsequent dehydrogenation cf the normal butenes to butadiene in a second dehydrogenation step. When this is the case a C4 fraction may be passed from pipe I82 through pipe Ho controlled by valve III to a second dehydrogenation unit I I2 operated so as to produce from butenes charged thereto optimum yields of butadiene. The dehydrogenation eilluent is passed from unit I it through a pipe i l3 controlled by a valve I I to a suitable separator I I5. Hydrogen and other material lighter than 04 hydrocarbons are removed through pipe 55% controlled by valve iii. A C4 fraction containing a substantial amount of butadiene is removed through pipe H8 and may be discharged 7 from the system through valve IIi'l. If desired this material may be introduced directly to reaction chamber 35 through pipe 52. This mixture may be treated in fractionating column I2 by being passed from N8 through pipe I28 controlled by valve I2! to pipes 565 and It and fractionating column I2 for treatment as has been discussed. Material higher boiling than C4 bydrocarbons may be removed from separating myeans M5 through a pipe I22 controlled by valve 51.3.

As has been discussed the kettle product of fractionating column I2 will contain substantial amounts of normal butenes which will find their way to separating unit 69. These normal butenes may be recovered by means of separating unit 63 in a more or less concentrated form and maybe passed therefrom through pipe I24 controlled by a valve I25 directly to the pipe III! and the dehydrogenation unit H2. In some instances it may be desirable to have the normal butenes produced by the dehydrogenation unit 92 in a more concentrated condition before they are charged to the dehydrogenation unit I I2. When this is the case the C4 fraction passing through pipe H32 may be removed through pipe I30 controlled by a valve MI and passed to suitable olefin concentration means represented by a fractional distillation column I 32. Olefins may be separated from the parafiins in a more concentrated form in fractional distillation column I32 by distillation in the presence of sulfur dioxide in a manner disclosed in the previously mentioned Patent 2,186,524, Sulfur dioxide for this purpose may be introduced through a pipe I33 controlled by a valve I 34. The fractionation may be aided by suitable packing or the like not shown, by heating means represented by heating coil I35, and by cooling and reflux means illustrated by cooling means I36. A paraflin-containing mixture is removed as a low boiling fraction through pipe I3! and may be discharged from the system through a valve I38 or may be passed entirely or in part from pipe I 31 through pipe Il) controlled by a valve II to pipe 22 and separating unit 24. A higher boiling, olefin-containing fraction, which may or may not contain sulfur dioxide, is re-= moved from fractionating column I32 through a pipe I42 and may be discharged through a valve I43 or may be passed, as Will generally be the case, from pipe I42 through pipe I 44 controlled 9 by'a valve I45. If this material is suitably free ofsulfur dioxide, it may be passed on through pipe M l and valve I46 directly to pipes I24 and I I and dehydrogenation unit I I2. In most cases,

however, this material will contain an appreciable amount of sulfur dioxide, in which case it may be passed from pipe I I-I through pipe I l'I controlled by a valve I48 to pipe 58 and separating unit 60.

In some instances a hydrocarbon fraction containing appreciable amounts of normal butenes may be introduced to the system through pipe I50 controlled by a valve II and leading to pipe I24. When such a fraction contains substantial amounts of normal butane or the like which should be removed, the material may be passed from pipe I50 through pipe I52 controlled by a valve I53 leading to pipe I30 and olefin concentrating means I32. In some instances such a material may constitute the sole source of charge to our process.

The dehydrogenation unit 92 and the dehydrogenation unit I I2 will be comprised of suitable heating units or furnaces, catalyst chambers, and the like, known to the art for effecting and maintaining catalytic, substantially nondestructive dehydrogenation of low boiling hydrocarbons. While it may be found possible to effect one or both of the dehydrogenations in the absence of a catalyst, we prefer to employ catalytic dehydrogen-ation for most of the charge stocks which will be introduced to our process, using any suitable dehydrogenation catalyst or catalysts. As is known, the catalyst chambers may be so arranged that heat is supplied to the catalyst body or bodies and to the reacting mixture to keep the reaction at a desired level. Stationary masses of granular catalysts may be used, or flowing masses of finely owdered solid catalysts may be employed, or other modifications of catalytic dehydrogenation may be employed as will be found most suitable. While the various fractional distillation units have been shown as single fractional distillation columns it is to be understood that this is merely diagrammatic and any of them may comprise two or more fractional distillation columns accompanied by conventional supplementary equipment as will be readily understood by one skilled in the art. Additional pumps, heaters, coolers, meters, flow controllers, temperature indicating and controlling equipment, reflux equipment, and the like, may be included and supplied by one skilled in the art in connection with any specific modification or installation in the light of the detailed discussions of material flows, reaction conditions, fractions desired, and 4 material streams to be separated which are dis- I invention, a normal butane fraction separated closed and discussed herein. Isobutane, and/or isobutene may be found to be present in one or more of the C4 fractions being treated, or may be introduced purposely through pipe 30, as discussed. Such iso C4 hydrocarbons can be removed through pipes 21, I00, H6, 6|, and/or 53, as will be appreciated.

Other low-boiling diolefins can also be produced by our process, especially isoprene and cyclopentadiene. Piperylene is generally more readily separated from accompanying hydrocarbons, and its production will not require such elaborate treatment in most cases. While sulfur dioxide will react with C5 diolefins to produce a diolefin-sulfone, it is not so well suited for use in connection with separating means I2 or I32. Therefore, when treating C5 hydrocarbons to produce C5 diolefins, other saturateunsaturate separation steps known to the art should be substi- 10 tuted, the operation of reaction chamber 35 and immediately subsequent equipment remaining as described.

Example I As an example of one method of practicing our from natural gas is dehydrogenated in dehydrogenation unit 92, in admixture with a recycle normal butane fraction, at a low superatmospheric pressure and a temperature of about 1050 F. in the presence of a mass of granular dehydrogenation catalyst prepared by impregnating bauxite with chromium oxide, the flow rate being maintained between about 1 and 2 liquid volumes of butane per volume of catalyst per hour. The efiiuent, which contains a substantial quantity of butenes and a small amount of butadiene, is cooled and condensed to recover a C4 fraction, which is passed from separating unit 9'! to the fractionating column I2, wherein distillation takes place in the presence of added sulfur dioxide. A butane-sulfur dioxide fraction is removed as a low-boiling fraction and passed to separating unit 2 8, in which a. normal butane fraction is recovered and passed to dehydrogenation unit 92 as the recycle normal butane fraction. A highboiling, butenes-containing fraction is removed from fractionating column I2, and a normal butene fraction is recovered therefrom by employing reaction chamber 35, flash vaporizer 50, and separating unit 60. This normal butene fraction is dehydrogenated in dehydrogenation unit II 2 in the presence of a granular catalyst which consists of bauxite treated with an alkali which leaves an alkaline residue, the dehydrogenation temperature being about 1200 F. Methane is added to maintain a total pressure slightly above atmospheric and an initial partial pressure of normal butenes of about 3 pounds per square inch absolute, and the flow rate is about 1.5 liquid volume of butenes per volume of catalyst pe hour. By means of separating unit II5 a C4 fraction, containing between 15 and 20 per cent butadiene, is separated from the dehydrogenation efiluent and also passed to the fractionating column I2. The high-boiling, butenes-containing fraction removed from fractionating column I2 also contains the butadiene produced by the process. This fraction is passed through reaction chamber 35 at a temperature of about 70 C. in the presence of an excess of sulfur dioxide, the time being such that substantially complete conversion of the butadiene to the monomeric butadiene-sulfone is effected. The efiiuent is passed to the flash vaporizer 50, which is maintained at about C. and a subatmospheric pressure. Vaporous material is removed by compressor 55 to separating unit 60, a normal butene fraction being recovered therefrom for subsequent treatment as has been described. The residual butadiene-sulfone is removed as a liquid from flash vaporizer 50 by pump 68, and is heated in coil 70 to about C. to effect decomposition of the butadiene-sulfone, and butadiene is recovered in a substantially pure state through pipe 82as a product of the process.

Example II As a modification of the practice of the invention as in Example I, the dehydrogenation of normal butane is carried out at a temperature of about 950 F. in the presence of a granular chromium oxide gel, which contains about an equimolar amount of alumina and is prepared in the 11 manner disclosed in U. s. Patent 2,093,959, the dehydrogenation efliuent containing practically no butadiene. The C4 fraction from the effluent of dehydrogenation unit H2, operated as in Example I, is not passed to fractionating column but is removed through pipe M8 and valve H9, and introduced directly into reaction chamber 35 through pipes 62 and id, along with the highboiling fraction from column 52 and an excess of sulfur dioxide passed through pipe as and valve ti. The efiluent of the reaction chamber 35 is passed through pipe to flash vaporizer 5E), and the remainder of the operation is s given in Example, I.

Example III As an example of another method of practicing our invention, a normal butane fraction is dehydrogenated in dehydrogenation unit 9 2 at a pressure of about 10 pounds per square inch gauge and a temperature of about 956 R, in the presence of a mass of granular chromium oxide gel, the flow rate being about two volumes of liquid butane per volume of catalyst per hour. The resulting C4 fraction from separator 91 is passed to olefin concentration unit I32. A normal butane fraction is separated and returned to dehydrogenation unit 32, and a normal butene fraction, containing some normal butane, is Separated and passed to dehydrogenation unit H2,

wherein catalytic dehydrogenation takes place to produce butadiene. The resulting C4 fraction is passed from separator H5 to fractionating column i2. Sulfur dioxide is added through valve Iii, and a small amount of normal butane is removed in the low-boiling fraction, which is passed to separating unit 24*. The fractionation column [2 is so operated that butadiene, concentrated in the kettle, is reacted with sulfur dioxide to form monomeric butadiene-culfone. The high-boiling fraction, containing butenes and the butadienesulfone, is passed directly from the bottom of fractionation column #2 to flash vaporizer 56. Vapors are passed to separating unit 69, and a normal butene fraction is recovered and also passed to dehydrogenation unit H2. Butadiene is recovered from decomposition of the butadiene-sulfone. V

Itwill be seen from these examples that our invention may be satisfactorily applied in several modifications. various preferred modes of operation, the limits so illustrated are not to be applied to limit unnecessarily the broader aspects of our invention. While the invention has been disclosed and discussed primarily in connection with continuous operation, intermittent operation of the invention, or of one or more parts of the combination process discussed, may at times be found advantageous and is not to be considered outside of the spirit of the disclosure and teachings. ductionof other diolefins may be accomplished in similar operations.

This application is a division of ou prior and copending application Serial No. 386,324, filed April 1, 1941.

.We claim:

1. The continuous process of separating aliphatic conjugated diolefins from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feeding said diolefin containing mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the While these examples illustrate 12 temperature of said zone between 68 and 80 C., maintaining said hydrocarbon mixture and sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free diclefin with sulfur dioxide in said zone to form the monosulfone, preventing formation of heteropolymeric reaction products of said diolefin and sulfur dioxid by continuously maintaining in said zone a branched chain monoolefin having the same number of carbon atoms per molecule as said diolefin in an amount corresponding to from 2 to 10' per cent of the total hydrocarbons present as the sole suppressor of such heteropolymeric reaction products; continuously removing the reacted mixture from said zone, and resolving the withdrawn reaction mixture into the sulfone and unreacted materials.

2. The continuous process of separating butadione from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feeding said butadiene-containing hydrocarbon mixture and from one-half to three times its Weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the'temperature of said zone between and C., maintaining said hydrocarbon mixture and sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free butadiene with sulfur dioxide in said zone to form the monosulfone, preventing formation of heteropolymeric, reaction" products of butadiene and sulfur dioxide by continuously maintaining in said zone isobutylene. in an amount corresponding to from 2' to 10 per cent of th total hydrocarbons present as the sole suppressor of such heteropolymeric reaction prod ucts, continuously removing the reacted mixture from said zone, and volatilizing the volatile unreacted materials from said removed reacted mixture at a. temperature not exceeding, C. to leave butadiene monosulfone addition product as a residue;

3. The continuous process of separating isoprene from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feeding said isoprene-containing hydrocarbon. mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone between 60 and. 80 C., maintaining said hydrocarbon mixture and sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free isoprene with sulfur dioxide in said zone to form the monosulfone, preventing formation of heteropolymeric reaction products of isoprene and sulfur dioxide by continuously maintaining in said zone unsym-methyl ethyl ethylene in an amount corresponding to from 2 to 10 per cent of the total hydrocarbons present as the sole suppressor of such heteropolymeric' reaction products, continuously removing the reacted mixture from said zone, and volatilizing the volatile unreacted. materialsfrom said removed reacted mixture at a temperature not.exceeding 100 C. to leave isoprene monosulfone addition product as a residue.

4. The continuous process of separating'piperylene from admixture with other close-boiling more saturated hydrocarbons which comprises 13 continuously feeding said piperylene-containing hydrocarbon mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone between 60 and 80 C., maintaining said hydrocarbon mixture and sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free piperylene with sulfur dioxide in said zone to form the monosulfone, preventing formation of heteropolymeric reaction products of piperylene and sulfur dioxide by continuously maintaining in said zone unsym-methyl ethyl ethylene in an amount corresponding to from 2 to per cent of the total hydrocarbons present as the sole suppressor of such heteropolymeric reaction products, continuously removing the reacted mixture from said zone, and volatilizing the volatile unreacted materials from said removed reacted mixture at a temperature not exceeding 100 C. to leave piperylene monosulfone addition product as a residue.

ating said column with a bottom temperature of 80 C. and a top temperature of 60 C., fractionally distilling in said column in such manner that substantially all of said butadiene and butene is concentrated in the bottom portion thereof in admixture with an excess of sulfur dioxide and said butane forms an azeotrope with sulfur dioxide, reacting substantially all of said butadiene with said sulfur dioxide in the bottom portion of said column to form butadiene monosulfone, continuously maintaining in said column a concentration of isobutylene in an amount corresponding to from 2 to 10 per cent of the total hydrocarbons present such as to prevent formation of heteropolymeric reaction products of butadiene and sulfur dioxide, and continuously withdrawing from said column an overhead of said azeotrope of butane with sulfur dioxide and a bottoms product containing said monosulfone and said butene and relatively free from unreacted butadiene.

6. The continuous process of separating piperylene from admixture with close-boiling pentene and pentane which comprises continuousl feeding said piperylene-containing mixture and from one-half to three times its weight of sulfur dioxide into a fractional distillation column, the amount of said sulfur dioxide being so much in excess of that molecularly equivalent to the diolefin present in said mixture that free sulfur dioxide is present in the bottom of said column at all times, operating said column with a bottom temperature of 80 C. and a top temperature of 60 C., fractionally distilling in said column in such manner that substantially all of said piperylene and pentene is concentrated in the bottom portion thereof in admixture with an excess of sulfur dioxide and said pentane forms an azeotrope with sulfur dioxide, reacting substantially all of said piperylene with said sulfur dioxide in the bottom portion of said column to form piperylene monosulfone, continuously maintaining in said column a concentration of unsym-methylethylethylene in an amount corresponding to from 2 to 10 per cent of the total hydrocarbons present such as to prevent formation of heteropolymeric reaction products of piperylene and continuously withdrawing from said column an overhead of said azeotrope of pentane with sulfur dioxide and a bottoms product containing said monosulfone and said pentene and relatively free from unreacted piperylene.

7. The continuous process of separating isoprene from admixture with close-boiling pentene and pentane which comprises continuously feeding said isoprene-containing mixture and from one-half to three times its weight of sulfur dioxide into a fractional distillation column, the amount of said sulfur dioxide being so much in excess of that molecularly equivalent to the di olefin present in said mixture that free sulfur dioxide is present in the bottom of said column at all times, operating said column with a bottom temperature of C, and a top temperature of 60 C., fractionally distilling in said column in such manner that substantially all of said iso prone and pentene is concentrated in the bottom portion thereof in admixture with an excess of sulfur dioxide and said pentane forms an azeotrope with sulfur dioxide, reacting substantially all of said isoprene with said sulfur dioxid in the bottom portion of said column to formisoprene monosulfone, continuously maintaining in said column a concentration of unsym-methylethylethylene in an amount corresponding to from 2 to 10 per cent of the total hydrocarbons present 1 such as to prevent formation of heteropolymeric reaction products of isoprene and continuously withdrawing from said column an overhead of said azreotrope of pentane with sulfur dioxide and a bottoms product containing said monosulfone and said pentene and relatively free from unreacted isoprene.

8. A continuous process of separating an ali-- phatic conjugated diolefin from admixture with close-boiling corresponding olefin and paraffin which comprises continuously feeding said diolefin-containing mixture and from one-half to three times its weight of sulfur dioxide into fractional distillation column, the amount of said sul fur dioxide being so much in excess of that molecularly equivalent to the diolefin present in said mix ure that free sulfur dioxide is present in the bottom of said column at all times, operating said column with a bottom temperature of 80 C. and a top temperature of 60 C. fractionally distilling in said column in such manner that substantially all of said diolefin and olefin is concentrated in the bottom portion thereof in admixture with an excess of sulfur dioxide and said paraffin forms an azeotrope with sulfur dioxide, reacting substantially all of said diolefin with said sulfur dioxide in the bottom portion of said column to form diolefin monosulfone, continuously maintaining in said column a concentration of branched-chain monoolefin co responding to said diolefin in an amount corresponding. to from 2 to 10 per cent of the total hydrocarbons present such as to prevent formation of heteropolymeric reaction products of diolefin and sulfur dioxide and continuously withdrawing from said column an overhead of said azeotrope of paraffln with sulfur dioxide and a bottoms product containing said monosulfone and said olefin and relatively free from unreacted diolefin.

9. The continuous process of separating aliphatic conjugated diolefins from a mixture containing sam together with other close-boiling more Saturated hydrocarbons which comprises continuously feeding said diolefin-containing mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone between 60 and 80 C., maintaining said hydrocarbon mixture and sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free diolefin with sulfur dioxide in aid zone to form the monosulfone, said diolefin-containing mixture containing an insufficient amount of branched chain moloolefin having the same number of carbon atoms per molecule as said diolefin to suppress formation of heteropolymeric reaction products of said diolefin and sulfur dioxide, continuously and separately introducing into said reaction zone branched chain monolefin having the same number of carbon atoms per molecule as said diolefin in amount. such as to continuously maintain in said zone an amount of branched chain monoolefin sufficient to prevent formation of such heteropolymeric reaction products, said branched chain monoolefin being the sole suppressor of such heteropolymeric reaction products in said reaction zone, continuously removing the reacted mixture from said zone and resolving the withdrawn reaction mixture into the sulfone and unreacted materials.

10. The continuous process of separating butadiene from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feedin said butadiene-containing mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone between 60 and 80 0., maintaining said hydrocarbon mixture and said sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free butadiene with sulfur dioxide in said zone to form the monosulfone, said butadiene-containing mixture containing an insufficient amount of isobutylen to suppress formation of heteropolymeric reaction products of butadiene and sulfur dioxide, continuously and separately introducing into said reaction zone isobutylene in amount such as to continuously maintain in said zone an amount of isobutylene sufficient to prevent formation of such heteropolymeric reaction products, said isobutylene being the sole suppressor of such heteropolymeric reaction products in said reaction zone, continuously removing the reacted mixture from said zone, and resolving the withdrawn reaction mixture into the sulfone and unreacted materials.

11. The continuous process of separating isoprene from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feeding said isoprene-containing mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone betw en 60 and C., maintaining said hydrocarbon mixture and said sulfurdioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantially all free isoprene with sulfur dioxide in said zone toform the monosulfone, said isoprenecontaining ,mixture containing an insufficient amount of unsym-methyl ethyl ethylene to suppress formation of heteropolymeric reaction products of isoprene and sulfur dioxide, continuously and separately introducing into said reaction zone unsym-methyl ethyl ethylene in amount such as to continuously maintain in said zone an amount of unsym-methyl ethyl ethylene suificient to ,prevent formation of such heteropolymeric reaction products, said unsym-methyl ethyl ethylene being the sole suppressor of such heteropolymeric reaction products in said reaction zone, continuously removing the reacted mixture from said zone, and resolving the withdrawn reaction mixture into the sulfone and unreacted materials.

12. The continuous process of separating piperylene from admixture with other close-boiling more saturated hydrocarbons which comprises continuously feeding. said piperylene-containing mixture and from one-half to three times its weight of sulfur dioxide into a reaction zone, the

amount of said sulfur dioxide being in excess of that molecularly equivalent to the diolefin present in said mixture, maintaining the temperature of said zone between 60 and 80 C., maintaining said hydrocarbon mixture andsaid sulfur dioxide in liquid phase in said zone by the maintenance of elevated pressure in said zone, reacting substantiall all free piperylene with sulfur dioxide in said zone to form. the monosulfone, said piperylene-containing mixture containing an insufficient amount of unsym-methyl ethyl ethylene to suppress formation of heteropolymerie reaction products of piperylene and sulfur dioxide, continuously and separately introducing into said reaction zone unsym-methyl ethyl ethylene in amount such as to continuously maintain in said zone an amount of unsym-methyl ethyl ethylene sumcient to prevent formation of such heteropolymeric reaction products, said unsym-methyl ethyl ethylene being the sole suppressor of such heteropolymeric reaction products in said reaction zone, continuously removing the reacted mixture from said zone, and resolving the withdrawn reaction mixture into the sulfone and unreacted materials.

13. The process of claim 9' wherein the amount of said branched chain olefin maintained in said zone is between 2 and 10 per cent of the total hydrocarbons present.

14. The process of. claim 10 wherein the amount of said isobutylene maintained in said reaction zone is between 2 and 10 per cent of the total hydrocarbons present.

15. The process of claim 11 wherein the amount of unsym-methyl ethyl ethylene maintained in said reaction zone is between 2 and 10 per cent of the total hydrocarbons present.

16. The process of claim 12 wherein the amount of unsym-methyl ethyl ethylene maintained in said reaction zone is between 2 and 10 per cent of the total hydrocarbons present.

FREDERICK E. FREY. ROBERT D. SNOW. 

